oa The emerging role of helicopter time domain EM systems

Helicopter time domain electromagnetic (H-TEM) systems are an emerging technology. The ability to integrate the great depth penetration of fixed-wing systems with the spatial resolution and conductance discrimination of helicopter frequency domain systems is an important development for the detection of discrete conductors.

H-TEM systems can be configured with multiple receiver coils to make their responses more diagnostic, such as the discrimination of thick from thin conductors. The use of a rigid geometry allows these systems to measure during the transmitter on-time where high conductance targets produce a stronger response.

In areas of conductive overburden, it is possible to remove much of the high amplitude response due to surface conductivity from deeper bedrock conductors by subtracting the off-time response from the corresponding on-time response. The resultant profiles are more diagnostic of bedrock conductors than are the late off-time channels from the same system at a lower base frequency.